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College Park, MD, United States

Kara E.,Institute of Astronomy | Fabian A. C.,Institute of Astronomy | Cackett E. M.,Wayne State University | Steiner J. F.,Institute of Astronomy | And 4 more authors.
Monthly Notices of the Royal Astronomical Society

Reverberation lags in active galactic nuclei (AGN) were first discovered in the NLS1 galaxy, 1H0707-495. We present a follow-up analysis using 1.3 Ms of data, which allows for the closest ever look at the reverberation signature of this remarkable source. We confirm previous findings of a hard lag of ~100 s at frequencies ν ~ [0.5-4] × 10-4 Hz, and a soft lag of ~30 s at higher frequencies, ν ~ [0.6-3] × 10-3 Hz. These two frequency domains clearly show different energy dependences in their lag spectra. We also find evidence for a signature from the broad Fe Ka line in the high-frequency lag spectrum. We use Monte Carlo simulations to show how the lag and coherence measurements respond to the addition of Poisson noise and to dilution by other components. With our better understanding of these effects on the lag, we show that the lag-energy spectra can be modelled with a scenario in which low-frequency hard lags are produced by a compact corona responding to accretion rate fluctuations propagating through an optically thick accretion disc, and high-frequency soft lags are produced by short light-travel delay associated with reflection of coronal power-law photons off the disc. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Sanfrutos M.,CSIC - National Institute of Aerospace Technology | Miniutti G.,CSIC - National Institute of Aerospace Technology | Agis-Gonzalez B.,CSIC - National Institute of Aerospace Technology | Fabian A.C.,Institute of Astronomy | And 4 more authors.
Monthly Notices of the Royal Astronomical Society

We present results obtained from the time-resolved X-ray spectral analysis of the Narrow- Line-Seyfert 1 galaxy SWIFT J2127.4+5654 during a ~130 ks XMM-Newton observation. We reveal large spectral variations, especially during the first ~90 ks of the XMM- Newton exposure. The spectral variability can be attributed to a partial eclipse of the X-ray source by an intervening low-ionization/cold absorbing structure (cloud) with column density NH = 2.0+0.2 -0.3 × 1022 cm-2 which gradually covers and then uncovers the X-ray emitting region with covering fraction ranging from zero to ~43 per cent. Our analysis enables us to constrain the size, number density and location of the absorbing cloud with good accuracy. We infer a cloud size (diameter) of Dc ≤ 1.5 × 1013 cm, corresponding to a density of nc ≥ 1.5 × 109 cm-3 at a distance of Rc ≥ 4.3 × 1016 cm from the central black hole. All of the inferred quantities concur to identify the absorbing structure with one single cloud associated with the broad line region of SWIFT J2127.4+5654. We are also able to constrain the X-ray emitting region size (diameter) to be Ds ≤ 2.3 × 1013 cm which, assuming the black hole mass estimated from single-epoch optical spectroscopy (1.5 × 107Mo), translates into Ds ≤ 10.5 gravitational radii (rg) with larger sizes (in rg) being associated with smaller black hole masses, and vice versa. We also confirm the presence of a relativistically distorted reflection component off the inner accretion disc giving rise to a broad relativistic Fe K emission line and small soft excess (small because of the high Galactic column density), supporting the measurement of an intermediate black hole spin in SWIFT J2127.4+5654 that was obtained from a previous Suzaku observation. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Kara E.,Institute of Astronomy | Fabian A.C.,Institute of Astronomy | Cackett E.M.,Wayne State University | Uttley P.,University of Amsterdam | And 3 more authors.
Monthly Notices of the Royal Astronomical Society

We use archivalXMM-Newton observations of Ark 564 and Mrk 335 to calculate the frequencydependent time lags for these two well-studied sources. We discover high-frequency Fe K lags in both sources, indicating that the red wing of the line precedes the rest-frame energy by roughly 100 and 150 s for Ark 564 and Mrk 335, respectively. Including these two new sources, Fe K reverberation lags have been observed in seven Seyfert galaxies. We examine the low-frequency lag-energy spectrum, which is smooth, and shows no feature of reverberation, as would be expected if the low-frequency lags were produced by distant reflection offcircumnuclear material. The clear differences in the low- and high-frequency lag-energy spectra indicate that the lags are produced by two distinct physical processes. Finally, we find that the amplitude of the Fe K lag scales with black hole mass for these seven sources, consistent with a relativistic reflection model where the lag is the light travel delay associated with reflection of continuum photons offthe inner disc. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Park K.H.,University of Maryland University College | Park K.H.,Carnegie Mellon University | Ricotti M.,University of Maryland University College | Ricotti M.,Joint Space Science Institute JSI
Astrophysical Journal

In this third paper of a series, we study the growth and luminosity of black holes (BHs) in motion with respect to their surrounding medium. We run a large set of two-dimensional axis-symmetric simulations to explore a large parameter space of initial conditions and formulate an analytical model for the accretion. Contrary to the case without radiation feedback, the accretion rate increases with increasing BH velocity v bh reaching a maximum value at v bh = 2c s, in 50 km s-1, where c s, in is the sound speed inside the "cometary-shaped" H II region around the BH, before decreasing as when the ionization front (I-front) becomes R-type (rarefied) and the accretion rate approaches the classical Bondi-Hoyle-Lyttleton solution. The increase of the accretion rate with v bh is produced by the formation of a D-type (dense) I-front preceded by a standing bow shock that reduces the downstream gas velocity to transonic values. There is a range of densities and velocities where the dense shell is unstable producing periodic accretion rate peaks which can significantly increase the detectability of intermediate-mass BHs. We find that the mean accretion rate for a moving BH is larger than that of a stationary BH of the same mass if the medium temperature is T ∞ < 10 4 K. This result could be important for the growth of seed BHs in the multi-phase medium of the first galaxies and for building an early X-ray background that may affect the formation of the first galaxies and the reionization process. © 2013. The American Astronomical Society. All rights reserved. Source

Zoghbi A.,University of Maryland University College | Zoghbi A.,Joint Space Science Institute JSI | Reynolds C.,University of Maryland University College | Reynolds C.,Joint Space Science Institute JSI | And 4 more authors.
Astrophysical Journal

Several X-ray observations have recently revealed the presence of reverberation time delays between spectral components in active galactic nuclei. Most of the observed lags are between the power-law Comptonization component, seen directly, and the soft excess produced by reflection in the vicinity of the black hole. NGC 4151 was the first object to show these lags in the iron K band. Here, we report the discovery of reverberation lags in the Fe K band in two other sources: MCG-5-23-16 and NGC 7314. In both objects, the 6-7 keV band, where the Fe Kα line peaks, lags the bands at lower and higher energies with a time delay of 1 ks. These lags are unlikely to be due to the narrow Fe Kα line. They are fully consistent with reverberation of the relativistically broadened iron Kα line. The measured lags, their time scale, and spectral modeling indicate that most of the radiation is emitted at 5 and 24 gravitational radii for MCG-5-23-16 and NGC 7314, respectively. © 2013. The American Astronomical Society. All rights reserved.. Source

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